Background: Late preterm infants (LPI) born between 34+0-36+6 weeks are a vulnerable group who undergo a critical and rapid period of brain growth during the last 6 weeks of gestation1. This growth, not shielded by natural in-utero protection, might result in neuronal networks developing differently to in-utero brain development had the pregnancy progressed to term. We hypothesise that clinically well late-preterm infants are neurologically more immature and at risk for future neurodevelopmental problems than their term-counterparts and this immaturity persists even when these infants reach Term Corrected Age (TCA). We aim to (1) characterise and contrast the neurodevelopmental profile of well LPI 12-72 hours from birth and at TCA and compare this with full term infants (FTI) (39+0-41+6 weeks) 12-72 hours from birth using the Hammersmith Neonatal Neurological Examination (HNNE) (2) obtain local reference ranges for the 34 items in the HNNE in an Asian population.

Methods: Well LPI and FTI without any ongoing clinical concerns were recruited over a 12-month period. Neurological examination was performed using the HNNE (34 items grouped into 6 subcategories- tone, tone patterns, reflexes, movements, abnormal signs and behaviour). LPI were assessed at 2 time-points; 12-72 hours of life and at TCA of 39+0-41+6 weeks while FTI were assessed once at 12-72 hours of life. Each item was assigned an optimality score of 0, 0.5 or 1, totalling up to 34. Examinations were performed midway between feeds with the infant settled and comfortable. Quantitative comparison of the neurobehavioural patterns between LPI and FTI was made using 2-sample t-tests.

Results: Two hundred and twelve clinically well infants (79 LPI and 133 FTI) were recruited. Mean optimality scores for LPI and FTI at 12-72 hours of life were 25.11/34 and 31.19/34 respectively, with a mean difference of 6.08 (p<0.0001). Mean optimality score for LPI on reaching TCA was 28.91/34, with a mean difference of 2.28 (p<0.0001) when compared to the FTI. This difference was most apparent in 2 subcategories – tone and movement with a median difference of 1.5 and 1 respectively when compared to their term counterparts (p<0.0001). Reference optimality scores for the 34 items on the HNNE for both FT and LP infants of our Asian dominant population were also obtained.

Conclusion: Our study demonstrated the neurological immaturity of LPI when compared to FT counterparts. This immaturity persists even on reaching TCA particularly in ‘tone’ and ‘movement’ subcategories. Our study also provides reference optimality scores for all 34 items in the HNNE for both FT and LP infants in an Asian population.